Adjustable potentiometer



March 31, 1959 E. BLANCO ADJUSTABLE POTENTI OMETER Filed Aug. v$50. 1955 2 Sheets-Sheet l March 3l, 1959 E. BLANCO 2,880,293

ADJUSTABLE POTENTIOMETER Filed'Aug. 30. 1955 2 Sheets-Sheet 2 electro-mechanical systems.

signments, to Daystrom, Incorporated, Murray Hill, NJ., a corporation of New Jersey Application August 30, 1955,V Serial No. 531,524 Claims. (Cl. 20148) This invention relates to potentiometer structures and particularly to a sub-miniature type potentiometer suitable for high voltage division in electronic, electric, and

Miniature potentiometers have been designed and used, the present invention being a potentiometer of this type which is accurate, reliable, economical to construct, and will remain in adjustment throughout extreme conditions of temperature, acceleration, shock, and vibration. It uses a casing having a substantially square exterior and ya cylindrical interior and is provided with a ball as a.

bearing and contact element to obtain a smooth adjust able action and a reliable contact.

The potentiometer unit is constructed so that after adjustments have been made, it may be sealed at a denite fixed position'. It utilizes a worm and pinion adjusting drive and resistance element havinga core on which a tine resistance wire is wound. It is approximately 1/2" square, 3/16 thick, and weighs less than two grams. The worm and pinion adjustment give a 40 to l ratio which assures excellent resolution and no-noise characteristics. Many units may be stacked together to form a compact bank. The same features to be described can be used in larger units to advantage.

The principal object of the invention, therefore, isv to facilitate the division of electrical voltages in a minimumsized potentiometer.

' Another object ofthe invention is to provide an improved sub-miniature type of potentiometer having adjustability with accuracy and reliability.

A further object of the invention is to provide within certain minimum over-all dimensions, a potentiometer capable of economic construction and of providing accurate and reliable operation.

The novel features which are believed to be characteristic of this invention, both as to the manner of its organization and the mode of its operation, will be better understood from the following description when read in conjunction with the accompanying drawings, in which:

Fig. l is a plan view of a potentiometer embodying the invention;

Fig. 2 is an end view of the unit shown in Fig. 1;

Fig. 3 is a cross-sectional view taken along the line 3 3 of Fig. 1;

Fig. 4 is an enlarged detail view of a portion of the unit shown in Fig. l and taken along the line 4 4 of Fig. l;

Fig. 5 is an enlarged detail view taken along the line 5 5 of Fig. l;

Fig. 6 is a cross-sectional view showing the worm and gear drive elements of the invention and taken along the line 6 6 of Fig. 3;

Fig. 7 is a cross-sectional view taken along the line 7 7 of Fig. 3; and

Fig. 8 is a cross-sectional view taken along the line- 8-8 of Fig. 3.

Referring now to the drawings in which the same numetals identify like elements, a casing 5 made of a heat- Patented Mar. 31, 1959 dissipating aluminum alloy has a substantially square external shape with a flattened terminal corner 6 and an internal circular recess 7. The casing is provided in diagonally opposite corners with holes 9 having axes extending parallel with the axis of the recess 7 for mounting the unit singly or in stacks. A radial hole is provided perpendicular to the surface 6 through which three electrical terminals pass within a plug 11. Two other holes are provided in the casing 5, one of which is shown at 12 for accommodating a shaft 13 having a worm gear 14 at one end thereof and a screwdriver slot 15 at the other end thereof. A third hole parallel with holes 9 and 10 the j:plug 11.

has a pin 17 positioned therein for axially locking and maintaining the worm shaft 13 in an operative assembled position as shown in Fig. 6.

Positioned within the circular recess 7 is an annular resistive element 19 which has a C-shaped conductive core 21 covered by an insulator 22 which will withstand a 1000 volt D.C. breakdown test and a wound resistance wire 23. The cylindrical' recess 7 is closed by a circular plate 25 which is held in the casing by peening over the edge 26 of the casing 5 to make the recess moisture proof. Mounted on a stub shaft portion 28 of the circular plate 25 is a fiber gear 29 having teeth 31, the teeth of the gear being in mesh with the worm 14 on the shaft 13. Mounted on the gear 29 and attached for rotation therewith is an electrical conducting plate 33 to which is attached a spring washer 34 having a bent portion 35 thereof in a slot in the circular plate 33. This insures vrotation of the washer 34 with the plate 33. To the opjposite side of the washer 34 from the portion 35 is electrically attached a precious metal Contact slider arm 37 ,in contact with the wire 23. The spring washer 34 and .slider arm 37 could be one piece.

In the center of the recess 7 and fixedly mounted to the lower face thereof is an insulating ring 38, on which as an electrical conducting support 39 having a tapered recess 41 therein. In the recess 41 is a metal ball 42, a portion of the upper side of which is accommodated in the hole in the plate 33. Thus, an electrical connection entends from the contact slider arm 37 in contact with Wirte 23, through the metal plate 33, through the ball 42, the support 39, and to a conductor 44 extending through The opposite ends of the resistance wire 23 :are electrically brought out through the plug 11 as shown at 45 and 46 in Figures 1 and 2. These connections to the ends of the wire 23 are mounted on pins -48 and 49, which are held in the holes 50 shown in Figure 2.

The above potentiometer construction is particularly suitable for miniature-sized potentiometers, and accurate -adjustability is obtainable through the worm and gear drive, providing a 4G to 1 ratio, and a ball bearing 42. By the use of a ball 42, a very low turning torque is required fon the shaft 13 while contacts of zero resistance are maintained between the ball and the plate 33 and the :support 39. Despite its sub-miniature size, its high accuracy vv'ill be maintained throughout broad environmental parameters.

I claim:

l. A subminiature potentiometer comprising a casing having .an internal recess therein with top and bottom walls; a wound wire resistive element seated in said recess adjacent the recess periphery; a support projecting from one of said walls of said recess and having an outer end spaced therefrom providing a bearing seat; a ball seated in said bearing seat; the other of said walls having a planar surface portion; a structure rotatably supported on said other of said walls and having a surface engaging said planar surface portion, said structure further having bearing engagement with said ball to be held in frictional supporting engagement with said planar surface portion by said ball; electrical connections with said resistive element including a slider contact carried by said structure to slidably, engage said resistive element, said slider contact being electrically connected through said structure and said ball to said support to provide an velectrical terminal for said slider contact at said support; and manually operable means drivingly engaged with said structure and extendingl outwardly through a Aside wall of said casing for rotating said structure from the exterior of said casing to vary the position of said slider contact on said resistive element.

2. A subminiature potentiometer comprising a casing having an internal recess therein with top and bottom walls; a C-shaped resistive element seated in said recess adjacent the recess periphery; said top wall having a unitary support projecting into said recess; a non-metallic gear rotatably mounted on said support; said top wall having a planar surface portion encircling said support; said gear having a surface engaging with said planar surface portion; means for forcing said gear toward said top wall to provide frictional engagement between said gear and said planar surface portion, including a bearing plate in the form of a disc having peripheral edge engagement with the peripheral margin of said gear, said disc having a central opening; conductive bearing means positioned at the center of curvature of said resistive element and insulated therefrom, said bearing means engaging the said central opening of said disc; electrical connections with said resistive element including a slider contact carried by said plate to slidably engage said resistive element; and manually operable means including a worm meshing with said gear for rotating said gear and plate as a unit from the exterior of said casing to vary the position of said slider contact on said resistive element.

3. A subminiature potentiometer as recited in claim 2 wherein said conductive bearing means includes a support projecting into said recess from said bottom wall and axially aligned with said first mentioned support, and

having an internal circular recess and a cover plate affixed thereto enclosing said recess; a worm screw rotat- ,ably positioned in said casing to tangentially extend across a portion of the periphery of said recess; a C- shaped resistive element positioned within the periphery of said recess, each end of'said resistive element having a conductive lead connected thereto and extending through said casing for rst and second external electrical connections; conductive bearing means positioned at the center of curvature of said resistive element and insulated therefrom, said bearing means having a conductive lead for a third external electrical connection; a wiper assembly for slidably contacting any selected portion of said resistive element, said assembly including a nonconductive gear having teeth adapted to engage said worm screw, a resilient conductive element aixed thereto shaped to receive said bearing means and having a wiper portion extending radially to electrically contact said resistive element, said gear being spring biased into pressure contact with said casing cover plate by the engagement of said resilient conductive element with said bearing means; whereby positive electrical connection between said resistive element and said third external connection is provided and selective adjustment of said wiper portion by rotation of said worm screw is accurately maintained regardless of vibration and shock forces to which said potentiometer may be subjected.

5. A subminiature potentiometer as recited in claim 4 wherein said non-conductive gear is disposed in a iirst plane extending transversely of said circular recess, and said C-shaped resistive element and said conductive bearing means are generally positioned in a common plane within said recess which is spaced from and parallel to said rst plane.

References Cited in the le of this patent UNITED STATES PATENTS 586,864 Pieper July 20, 1897 1,938,396 Megow Dec. 5, 1933 2,125,954 Richter Aug. 9, 1938 2,141,770 Solomon Dec. 27, 1938 2,201,686 Marsten May 21, 1940 2,379,641 Keitel J'uly 3, 1945 2,504,906 Tremblay `Apr. 18, 1950 2,581,266 Lum Jan. l, 1952 2,622,174 Kling Dec. 16, 1952 2,687,463 Riley Aug. 24, 1954 

